378. 骑士放置

https://www.acwing.com/problem/content/submission/code_detail/16206815/

AcWing/378/378.cpp

@@ -0,0 +1,64 @@
+#include <iostream>
+#include <cstring>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 105;
+const int dx[] = {2, 2, -2, -2, 1, 1, -1, -1},
+          dy[] = {1, -1, 1, -1, 2, -2, 2, -2};
+
+int n, m, t, ans;
+std::pair<int, int> match[N][N];
+bool disabled[N][N], vis[N][N];
+
+bool dfs(int x, int y) {
+    for (int i = 0; i < 8; i++) {
+        int xx = x + dx[i],
+            yy = y + dy[i];
+
+        if (xx < 1 || xx > n || yy < 1 || yy > m) continue;
+        if (disabled[xx][yy] || vis[xx][yy]) continue;
+
+        vis[xx][yy] = true;
+
+        auto t = match[xx][yy];
+
+        if (!t.first || dfs(t.first, t.second)) {
+            match[xx][yy] = std::make_pair(x, y);
+            return true;
+        }
+    }
+
+    return false;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m >> t;
+
+    for (int i = 1; i <= t; i++) {
+        int x, y;
+
+        cin >> x >> y;
+
+        disabled[x][y] = true;
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            if (disabled[i][j] || (i + j) % 2) continue;
+
+            memset(vis, 0x00, sizeof(vis));
+            if (dfs(i, j)) ans++;
+        }
+    }
+
+    cout << n * m - t - ans << endl;
+
+    return 0;
+}